It is estimated that at least 1.7 trillion barrels of heavy crude oil (sometimes referred to as bitumen) exists in the oil sands of northern Alberta, Canada. Oil sands are naturally occurring mixtures of sand or clay, water, and an extremely dense and viscous form of petroleum called bitumen. The bitumen extracted from oil sands is viscous, solid, or semisolid in form and is difficult to transport because it does not easily flow at temperatures normally encountered in an oil pipeline. Despite such transport difficulties and costs to process into gasoline, diesel fuel, and other products, oil sands are being mined on a vast scale to extract the bitumen, which may be converted into synthetic oil or refined directly into petroleum products.
Considerable amounts of this resource are mined by truck and shovel operations. Constituents of the mined material include bitumen, sand, clay, and water. A common method to initiate bitumen liberation from the sand grains is hydrotransport, where the crushed ore is mixed with hot water to create a slurry that is pumped by pipeline to a bitumen extraction plant. Due to the high shear and mixing imparted on the slurry in the pipeline, as well as aeration by means of either turbulent mixing or air injection, the oil sands become conditioned. This conditioning causes the bitumen to recede from the coarse solids and become aerated. A primary separation cell (PSC) is used to separate the coarse solids from the aerated bitumen.
The high shear of hydrotransport, along with addition of caustic when necessary to enhance bitumen recovery, causes the fines (defined as solid particles less that 44 micrometers in diameter) to become dispersed. While such dispersion of fines assists with bitumen recovery, it also causes other problems, one of which is a portion of the fines and clays (solids less than 2 micrometers) reporting to the bitumen froth layer. To reduce the mass of solids reporting to the bitumen froth, the bitumen droplets rise through a quiescent layer of water, termed the underwash water, just prior to forming the froth layer. The quiescent layer is achieved by introducing water directly below the formed bitumen froth layer (e.g., U.S. Pat. No. 3,847,789). The underwash layer enables some of the solids that have floated up with the bitumen to be washed back down into the middlings layer. Processing ores that contain high fines have historically led to poor froth quality as more solids are carried into the froth thus impacting secondary bitumen extraction by potentially plugging up the froth treatment equipment and causing the process to shut down and/or increasing the load on downstream froth treatment unit operations.
U.S. Patent Application Publication No. 2005/0194292 discloses a method to improve bitumen recovery from oil sands by adding a processing aid capable of sequestering cations. The bitumen is contacted with the processing aid before primary separation of the bitumen from the mineral matter. This patent application discloses dosing the processing aid prior to primary separation of the bitumen from the mineral solids.
PCT Patent Application WO 2009/089570 discloses a two-polymer system that floats aggregated mineral matter. The first polymer is hydrophilic and intended to minimize heterocoagulation between two different types of particulate matter and/or liquid droplets. The second polymer is hydrophobic and absorbs preferentially to either the solids or the liquid matter to induce hydrophobic aggregation.
Chemical programs known in the prior art propose chemical addition at the ore preparation or hydrotransport stages of the process and are generally not cost-effective due to the large dosages that would be necessary to impart any improvement on bitumen recovery or froth quality. As a result, oil sands producers currently do not use specialty chemicals to enhance bitumen recovery or improve froth quality. There thus exists an industrial need for targeted application of specialty chemicals to improve bitumen recovery and enhance froth quality from oil sands extraction processes. A particular benefit of such targeted applications is that the specialty chemicals will not be consumed by coarse sand particles, and the dosage of the chemicals can be reduced to make them economically feasible.